One of the most common orthopedic problems in dogs is injury to the stifle (hind knee) joint, and in particular, the cranial cruciate ligament of the stifle joint. Referring to FIGS. 1 and 3A, the canine stifle joint 10 is a hinge joint and includes the femur 20, the patella 15 (illustrated in FIG. 3A), and the tibia 30. Holding these bones together are the cranial cruciate ligament 40, the caudal cruciate ligament 50, the medial collateral ligament 60, the lateral collateral ligament 70, and the patellar tendon (not illustrated). The stifle joint 10 also includes the lateral meniscus 80 and the medial meniscus 90. The joint is bathed in synovial fluid which is contained in the joint capsule. The cruciate ligaments reside deep within the knee joint, and the cranial cruciate ligament is much more commonly injured than the other ligaments of the canine stifle. Dogs with injuries will suffer lameness, pain, and develop associated disorders.
The causes of cruciate ligament injury can be complex. In some cases, injury can be through sudden rotation of the stifle. However, other cases can develop through no apparent trauma. It is believed that the slope of the tibial plateau along with the joint forces causes the femur to translate upon the tibial plateau. This results in a classic condition known as cranial tibial thrust. This forward movement puts the cranial cruciate ligament under significant stress and can result in attenuation or rupture of the cranial cruciate ligament.
When either the caudal or cruciate ligament does attenuate or is ruptured, it can lead to joint instability, and if left untreated it will result in progressive degenerative changes within the joint. In some cases, ligament rupture can lead to articular wear of the joint secondary to the femoral condyle engaging upon the tibial plateau and causing articular “scuffing.” These forces continue to cause degeneration and weakening of secondary restraints such as the medial and lateral meniscus. The instability can lead to tears of the medial and lateral meniscus, which can cause further instability, pain, and lameness. In addition, as joint changes develop, the cruciate ligaments undergo alteration in their microstructure. Collagen fibrin become hyalinized, and the tensile strength of the ligament is reduced, making the ligament more susceptible to damage from minimal trauma.
Currently, a number of extracapsular and intra-articular surgical techniques can be used to treat stifle ligament injuries. Extracapsular techniques include imbrication of the lateral joint tissues with one or more sutures. The sutures are placed in a general anteroposterior orientation to eliminate the cranial displacement of the tibia on the femur (cranial drawer). By placing the imbrication suture or sutures on the lateral aspect of the joint, the tendency for inward rotation of the tibia due to cranial cruciate ligament insufficiency is also prevented. However, current extracapsular imbrication procedures are limited in the ability to provide sufficient stability to the cranial cruciate deficient stifle joint, and are also met with limited success in larger dogs.
Intra-articular repairs include reconstruction or replacement of the cruciate ligaments with either an autogenous or a synthetic graft. Replacement techniques involve the re-creation of an intra-articular structure in the approximate spatial orientation of the normal cranial cruciate ligament. The graft is usually passed through drill holes in the femur and tibia and, depending on the technique used, is attached to the soft tissues of the femur or tibia. Not only are such techniques invasive, but the ideal transplant material has not yet been found. Ideally, a material would possess great strength, some elasticity, and tolerate wear and tear in the joint for years, and be non-irritant.
Another intra-articular technique includes tibial plateau leveling osteotomy (TPLO) where the tibia is cut and the slope between the femur and tibia reduced. A tibial tuberosity advancement (TTA) procedure is yet another intra-articular procedure. These procedures can result in surgical complications, however, such as infection, bleeding, nonunion, loosening or fracture of hardware, arterial and nerve injury, severe limitation in joint movement, chronic pain, and continued instability.
Injury to the cranial cruciate ligament of the canine stifle joint is a particularly acute problem. Every year in the United States approximately 1.4 million dogs have cranial cruciate ligament deficiencies requiring surgery. Pet owners spend approximately $1.5 billion dollars on repairs to the cranial cruciate ligament as of 2006. The current surgical procedures to repair the ligament, including TPLO and TTA, can result in significant intra-articular damage and create fibrosis to the articular surface. In the best case scenario, the change in the inclination of the tibial tuberosity and this fibrosis results in a less painful and more stable knee, allowing the dog to recover from the surgical insult and continue with normal activities. However, anywhere from 50% to 75% of the dogs who tear their cranial cruciate ligament will also have a contralateral cranial cruciate ligament injury within two years.
Thus, the current technology from a standpoint of surgical intervention requires significant intra-articular and accurate bony osteotomies to be performed in order to achieve a successful outcome. Given the high number of canine ligament injuries and the complications associated with current surgical procedures, there is a need for a minimally invasive and less destructive intra-articular or extra-articular surgical procedure to treat injured ligaments of the canine stifle joint.